Kind or concentration of blood components, such as metabolites, proteins, lipids, electrolytes, enzymes, antigens, and antibodies, is measured, in general, using a plasma or serum sample obtained by centrifuging whole blood. However, centrifuging takes labor and time. Particularly, centrifuging is unsuitable for an urgent case of measuring a small number of samples promptly and on site inspection, because of requiring a centrifuge and electricity. Thereupon, it has been investigated to separate plasma or serum from whole blood by filtration.
Several filtration methods using glass fiber filter have been known wherein whole blood is charged into glass fiber filter contained in a column from one side of the column and pressurized or sucked to obtain plasma or serum from the other side (Japanese Patent KOKOKU Nos. 44-14673, 5-52463, Japanese Patent KOKAI Nos. 2-208565, 4-208856).
However, practical filtration methods capable of obtaining an amount of plasma or serum from whole blood necessary for measuring by an automatic analyzer have not been developed except a part of items, such as blood sugar.
On the other hand, inventors belonging to the assignee of this application have developed a plasma or serum filtering unit comprising a filter element containing a combination of glass fiber filter and porous membrane and a baffle narrowing aperture of the filter element at an exit of a filtrate passage, with which plasma or serum can be separated effectively ever from a small quantity of whole blood (U.S. Pat. No. 5,979,669).
Further, these inventors have developed a blood-filtering unit comprising a injection needle for drawing blood at an inlet of the blood-filtering unit and a filtrate receiver connected to an exit of a filtrate passage (U.S. Pat. No. 5,996,811).
But the unit was unsatisfactory for practical use in terms of uneasy operation or handling, since it required a sucking adaptor or syringe connected with the blood-filtering unit to collect and filter blood instantaneously.
Further, a device comprising a vacuum blood-drawing tube containing a injection needle at a front edge of it and accommodating a blood-filtering unit in it, a vacuum tube to suck in filtered serum or plasma, and a part with two injection needles connecting the vacuum blood-drawing tube and the vacuum tube has been developed to separate serum or plasma from whole blood (Japanese Patent KOKAI Nos. 4-208856, 5-93721, 5-188053).
But operation of this device is troublesome too. Because three injection needles contained in the device must be stung in correct order to connect four parts of the device.